This invention relates to a device for controlling evaporative emission from an automobile.
If fuel evaporated from a fuel tank of an automobile and/or a combustible gas mixture preparing device, such as a carburetor, is emitted into the atmosphere, air pollution is caused due to hydrocarbons contained in the fuel. Devices are known which control evaporative emission so as to prevent air pollution due to the evaporated fuel and which prevent evaporative fuel loss from an automobile. For example, a device, described in Japanese Patent Publication No. 19729-78, for controlling the evaporative emission from a fuel tank communicated with an internal combustion engine comprises: a casing which accomodates fuel gas absorbing agents; a tank port which is disposed on the casing and which is adapted to communicate with the fuel tank, and which has two check valves in parallel therein for permitting the flow of fuel gas from the fuel tank into the casing and from the casing into the fuel tank , respectively, and; a purge port which is disposed on the casing and which is adapted to communicate with an internal combustion engine mounted in an automobile, and which has a check valve therein for permitting the flow of fuel gas from the casing to the engine. This device can control evaporative emission. This is because, when the pressures in the fuel tank and intake passage of the internal combustion engine become vacuums, some of the check valves are open so that evaporated fuel from the fuel tank and a float chamber of the carburetor is temporarily stored in the absorbing agents in the casing. Control can also be achieved because, when the engine is restarted, another check valve, which has been closed while the engine is stopped, is open due to the intake vacuum, so that fuel gas stored in the absorbing agents is purged and discharged into the intake passage of the engine, and then, the purged fuel gas is burnt in the combustion chambers of the engine. As a result, emission of hydrocarbons into the atmosphere and air pollution caused thereby are prevented.
However, if the device described in the above mentioned prior art is made entirely of a metal, such as steel plate or die cast aluminum, the weight of the device becomes very heavy, and the cost of the device becomes high since a number of manufacturing steps are needed. In addition, in the device, the tank port and the purge port have valve members mounted in the ports thereof for supplying vacuum. Since the valve members are separately constructed from the casing and are accomodated into the casing, the manufacturing cost of the valve members is also high.
To overcome the above mentioned problems attempts have been made to manufacture the device of plastic, so that the weight and the cost of the device would both be low. However, since the valve seats of the check valves of the device are also made of the plastic, the durability of the valve seat is not satisfactory, and therefore, the device cannot actually be utilized.